Study: Coos Bay region in danger of megaquake

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Structures like the Coos Bay bridge are among the major infrastructure that will face risks when a subduction zone earthquake strikes the Pacific Northwest. (Photo by Lynn Ketchum, courtesy Oregon State University)

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CORVALLIS, Ore. – The Southern Oregon coast is in danger of a major earthquake in the next 50 years, scientists at Oregon State University said in a study released Wednesday.

The study, written by researchers at OSU and published by the U.S. Geological Survey, concludes there is a 40 percent chance of an earthquake in the Coos Bay, Ore. region that could be nearly as devastating as the earthquake in Japan in March of 2011.

The Cascadia Subduction Zone, off the Pacific Northwest Coast, has had many earthquakes over the past 10,000 years, according to Chris Goldfinger, who authored the study. He says the Southern Oregon coast may be the most vulnerable based on the history of recurring quakes in the region.

“The southern margin of Cascadia has a much higher recurrence level for major earthquakes than the northern end and, frankly, it is overdue for a rupture,” said Goldfinger, who is also a professor in OSU’s College of Earth, Ocean and Atmospheric Sciences. “That doesn’t mean that an earthquake couldn’t strike first along the northern half, from Newport, Ore. to Vancouver Island.”

The research may eventually lead to an update in Oregon’s building codes, researchers said.

The study took four years to complete and is based on 13 years of research.

“Over the past 10,000 years, there have been 19 earthquakes that extended along most of the margin, stretching from southern Vancouver Island to the Oregon-California border,” said Goldfinger. “These would typically be of a magnitude from about 8.7 to 9.2 – really huge earthquakes.

“We’ve also determined that there have been 22 additional earthquakes that involved just the southern end of the fault," he added. "We are assuming that these are slightly smaller – more like 8.0 – but not necessarily. They were still very large earthquakes that if they happened today could have a devastating impact.”

Jay Patton, who co-authored the study, said the clock is ticking on when a major earthquake will strike next.

“By the year 2060, if we have not had a major earthquake, we will have exceeded 85 percent of all the known intervals of earthquake recurrence in 10,000 years,” said Patton. “The interval between earthquakes ranges from a few decades to thousands of years, but we have already exceeded about three-fourths of them.”

The last major earthquake in the Pacific Northwest struck on Jan. 26, 1700. According to Goldfinger, written records in Japan say an ensuing tsunami destroyed that year’s rice crop that was stored in warehouses.

Patrick Corcoran, a hazards outreach specialist with OSU’s Sea Grant Extension Program, says residents along the west coast need to be prepared for a devastating earthquake.

“Now that we understand our vulnerability to mega-quakes and tsunamis, we need to develop a culture that is prepared at a level commensurate with the risk,” said Corcoran. “Unlike Japan, which has frequent earthquakes and thus is more culturally prepared for them, we in the Pacific Northwest have not had a mega-quake since European settlement. And since we have no culture of earthquakes, we have no culture of preparedness.”